The present invention is directed to a rock drill with an axially extending shank having a drill head at one end and a chuck end at the other, the shank comprises at least one conveying helical groove in its outside surface and a corresponding helical land forming the outside diameter of the shank with other grooves located in the land.
The conveying helical grooves in the shank of known drills transport the drillings removed during the drilling operation analogous to a conveying worm, moving the drillings from the deepest part of the borehole to the outside. At the present time such rock drills are used in ever smaller drilling tools where the output is increased by striker or impact energy. The rotational power requirement resulting from, among other things, friction between the land of the conveying groove and the borehole wall has remained essentially constant, since a reduction of the total land width of such drills would have a detrimental effect on the guidance of the rock drill in the material in which it is used.
There is a known rock drill in DE-AS 20 13, 327 where the shank has a conveying groove with a land having other grooves arranged to be spaced in the circumferential direction and inclined with respect to the axis of the drill.
In the broadest sense, this known rock drill has a reduction in the land surface cooperating with the borehole wall. A power gain obtained by less friction of the land against the borehole gain obtained by less friction of the land against the borehole wall due to the smaller land surface is lost in that the protuberant part of the other grooves shape, due to the hang-up with the in part rough surface of the borehole wall, thus increases the overall friction of the rock drill.